calling all the engineer types. (1 Viewer)

[gabe_j]

ok so i need to verify my work. as my inhouse engineers aren't well "in" at the moment.

i've got a 14' jib crane 10 feet off the ground under the boom. my max load is 500 lbs and the base of the crane is 24" with a 1'9" bolt circle using 3/4" redhead anchor bolts. each bolt as a pullout force of 10,561psi held by a concrete compressive strength of 3000psi at 8" thick actual mounting would be about 5" deep.

i'm calculating a 7000 lbs pull force on the far end of the base. thats 3500 lbs of excess support keeping my crane firmly in the ground.

anyone else care to run the numbers? don't worry i won't hold you liable i just want to double check my work. hopefully i'm right. ha

thanks to anyone thats willing to try and figure that out.

 

[gabe_j]

ok thanks for the views but I redid the math and so did my engineer and it works with a safety ratio of 3:1!!!

mod please close

 

[karlo]

I'm still trying to figure out what a jib crane is

 

[gabe_j]

one of these guys.

 

[mario8402]

whoa almost looks like the inside of our fab shop.

 

[gabe_j]

oh thats not my shop just posted a googled pic of a jib crane i don't have time to take a pic of my shop and load it.

 

[RocketSurgeon]

one of these guys.

This is ours:

The baby:

Her Mom:

Heading outside:

Our dinosaur:

 

[gabe_j]

nice man where are you working?

we have a small 5 ton overhead and a 10 ton overhead and jibs scattered around the other shop.

 

[DustinB]

As long as the anchor bolts are epoxied I wouldn't bat an eye.

 

[gabe_j]

I don't think they are expoxy type they are the ones with he expansion collar.

 

[DustinB]

Any time we set anchors for jibs up to 10'x10' span 1/2ton or less we use industrial epoxy with all-thread. Minimum of 6" concrete with 5'x5' clear defect-free surface. Can't comment on it from an engineering aspect though.

The bolt circle seems awfully small as well. The manufacturer we mainly use has a minimum bolt circle of 30" on a 36" base plate. I would be very careful. We have seen jibs fall over on people even with a large safety factor. Any time you use an anchor that is not encased in the slab you run more of a risk of defects in the substrate.

I sell cranes and hoists by the way, no engineering background other than electrical.

 

[gabe_j]

see now all the points you just brought up were concerns I brought up with my senior industrial engineers. and he got rather pissed I was second guessing him. I thought that the bolt circle was on the small side but I had a bigger issue not using an anchor block under the slab. the math says I've got a max moment of force of 7000 lbs each anchor bolt maxes out at 10,561 lbs till pull out.. but still somethin just rubs me the wrong way.

also there are some surface defects about 2 feet from the center of the column. I don't like that either.

 

[DustinB]

One thing to note is that this is not just a static load. People operating the hoist have a tendency to bump the control creating multiple shock loads. Also the load rolling towards the end of the beam and hitting the end stop can cause a significant shock load.

Is this a jib crane you guys manufactured? Is this a 6 or 12 bolt pattern?

I would at the very least suggest the epoxy anchors. At the end of the day though, it's going to be your senior engineer's signature holding the liability. Hopefully nothing bad happens though.

You might also look into the safety factors of some manufacturers. Most if not all maintain at least a 4 or 5 to 1 ratio. They still have the occasional failures.